1. Field of the Invention
The present invention relates to a receiving apparatus and transmitting apparatus for receiving and transmitting data as information light and a communication system using the same.
2. Description of the Related Art
As a communication system for transmitting data converted to optical information, optical information transmission systems using optical fibers as a transmission medium are in practical use.
In recent years, there has been remarkably progress in optical communication technology. Transmission of various kinds of information including image information by optical fibers is being realized to not only trunk lines, but also the level of the general homes, by links to not only telephone systems, but also computer networks.
The transfer rate has been improved enabling even communication at 100 Mbps and further 200 Mbps or 400 Mbps (on the frequency level, a giga-(G) hertz order, for instance, 2.4 to 5 GHz).
Summarizing the problem to be solved by the invention, when transmitting various kinds of information including image information by optical fibers to for example the general homes as explained above, the transmitted information is delivered to a personal computer, television, telephone, etc. (hereinafter, referred to as data processing apparatuses).
In this case, when the information processing apparatus is installed in one place, it is possible to lay an optical fiber inside the home for transfer of the optical information as it is to the information processing apparatus for example via an optical repeater and convert the optical information to an electric signal at the information processing apparatus side.
It is also possible to move the information processing apparatus around instead of installing it in one place, however, this is not practical in that it is then necessary to re-lay the optical fiber.
Use of wireless communication using radio waves can therefore be considered. Wireless communication is however only possible using the tens of Mbps to 100 Mbps range due to legal restrictions.
Accordingly, wireless communication cannot be applied for recent high speed optical communication of 100 Mbps or more.
Therefore, it is considered practical to convert an optical signal transmitted from the outside over an optical fiber to an electric signal by an optical repeater, convert the electric signal back to an optical signal to generate optical information (hereinafter, information light), and convert it back from an optical signal to electric signal at the information processing apparatus side.
A semiconductor laser and a light-emitting diode can be used for emitting information light, but a semiconductor laser is not preferable due to problems of directivity etc.
Accordingly, it is preferable to use a light-emitting diode. There are however official restrictions on the strength, and therefore problems remains in the strength per predetermined area. Under the current circumstances, construction of a communication system capable of reliably transmitting and receiving a high speed optical signal is difficult.